Camera tube with graded tellurium or arsenic target

Abstract

A camera tube target (9) which is to be scanned on one side by an electron beam (20), comprises a selenium-containing vitreous layer (21) also containing tellurium and arsenic. In order to improve various target characteristics and properties in accordance with the invention, the concentration of at least one of the elements tellurium and arsenic in a first sub-layer (25) of the selenium-containing layer (21), on the side to be scanned, increases toward the side to be scanned to a value at which the sum of the concentrations of tellurium and arsenic is at most 30 at. %. The arsenic concentration everywhere in the layer (21) exceeds 1.5 at. %. In a second sub-layer (26) adjoining the first sub-layer (25) the concentration of at least one of the elements arsenic and tellurium is smaller than its concentration an adjoining third sub-layer (27). A fourth sub-layer (28) may also be present between the third sub-layer (27) and the signal electrode (22). The concentration of arsenic and/or tellurium in the third sub-layer (27) is larger than its concentration in the fourth sub-layer.

What is claimed is: 
     
       1. A camera tube including an electron source and a target to be scanned on one side by an electron beam emanating from the source, said target comprising a vitreous layer containing the elements selenium, tellurium and arsenic, the concentration of at least one of these elements varying across the thickness of the vitreous layer, characterized in that said layer comprises a plurality of sub-layers, starting at the side to be scanned by the electron beam, including: (a) a first sub-layer in which the concentration of at least one of the elements tellurium and arsenic increases, toward the side to be scanned, to a concentration at which the sum of the concentrations of tellurium and arsenic is at most 30 atomic percent;   (b) a second sub-layer; and   (c) a third sub-layer in which the concentration of at least one of the elements tellurium and arsenic is larger than its concentration in the second sub-layer;   the arsenic concentration everywhere in the vitreous layer being larger than 1.5 atomic percent.   
     
     
       2. A camera tube as in claim 1, characterized in that the sum of the concentrations of arsenic and tellurium in the first sub-layer on the side to be scanned is larger than 8.5 at. %. 
     
     
       3. A camera tube as in claim 1 or 2, characterized in that the first sub-layer is thicker than 0.1 μm. 
     
     
       4. A camera tube as in claim 1 or 2, characterized in that the first sub-layer is thinner than 1 μm. 
     
     
       5. A camera tube as in claim 1 or 2, characterized in that the tellurium concentration in the second sub-layer is smaller than 4 at. %. 
     
     
       6. A camera tube as in claim 5, characterized in that tellurium is absent from the second sub-layer. 
     
     
       7. A camera tube as in claim 1 or 2, characterized in that said vitreous layer includes a fourth sub-layer wherein the concentration of at least one of the elements tellurium and arsenic is smaller than its concentration in the third sub-layer.